U.S. patent application number 13/052237 was filed with the patent office on 2011-10-06 for solid-state image sensor and imaging system.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Tadashi Sawayama.
Application Number | 20110242350 13/052237 |
Document ID | / |
Family ID | 44247834 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110242350 |
Kind Code |
A1 |
Sawayama; Tadashi |
October 6, 2011 |
SOLID-STATE IMAGE SENSOR AND IMAGING SYSTEM
Abstract
A solid-state image sensor including photoelectric conversion
elements, comprises a first insulating film arranged on a substrate
and having openings arranged on the respective elements, insulator
portions having a refractive index higher than that of the first
insulating film and arranged in the respective openings, a second
insulating film arranged on upper surfaces of the insulator
portions and an upper surface of the first insulating film, and a
third insulating film having a refractive index lower than that of
the second insulating film and arranged in contact with an upper
surface of the second insulating film, wherein letting .lamda. be a
wavelength of entering light, n be the refractive index of the
second insulating film, and t be a thickness of the second
insulating film in at least part of a region on the upper surface
of the first insulating film, a relation t<.lamda./n is
satisfied.
Inventors: |
Sawayama; Tadashi;
(Machida-shi, JP) |
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
44247834 |
Appl. No.: |
13/052237 |
Filed: |
March 21, 2011 |
Current U.S.
Class: |
348/222.1 ;
257/432; 257/E31.127 |
Current CPC
Class: |
H01L 31/02327 20130101;
H01L 27/14621 20130101; H01L 27/14625 20130101; H01L 27/14629
20130101 |
Class at
Publication: |
348/222.1 ;
257/432; 257/E31.127 |
International
Class: |
H04N 5/228 20060101
H04N005/228; H01L 31/0232 20060101 H01L031/0232 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 6, 2010 |
JP |
2010-088192 |
Feb 9, 2011 |
JP |
2011-026532 |
Claims
1. A solid-state image sensor including a semiconductor substrate
containing a plurality of photoelectric conversion elements, the
sensor comprising: a first insulating film which is arranged on the
semiconductor substrate and has a plurality of openings, each of
the plurality of openings being arranged on one of the plurality of
photoelectric conversion elements; a plurality of insulator
portions which have a refractive index higher than a refractive
index of the first insulating film, each of the plurality of
insulator portions being arranged in one of the plurality openings;
a second insulating film which is arranged on upper surfaces of the
plurality of insulator portions and an upper surface of the first
insulating film; and a third insulating film which has a refractive
index lower than a refractive index of the second insulating film
and is arranged in contact with an upper surface of the second
insulating film, wherein letting .lamda. be a wavelength of light
entering the plurality of insulator portions, n be the refractive
index of the second insulating film, and t be a thickness of the
second insulating film in at least part of a region on the upper
surface of the first insulating film, a relation t<.lamda./n is
satisfied.
2. The sensor according to claim 1, wherein the upper surface of
the second insulating film is a smooth continuous surface.
3. The sensor according to claim 1, wherein letting t1 be a
thickness of the second insulating film in at least part of a
region on the upper surfaces of the plurality of insulator
portions, t1>.lamda./n is further satisfied.
4. The sensor according to claim 1, wherein the opening has a
tapered shape in which an area increases with distance from the
photoelectric conversion element.
5. The sensor according to claim 1, wherein the second insulating
film and the insulator portion are formed from one of silicon
nitride and silicon oxynitride.
6. The sensor according to claim 1, further comprising a color
filter on the third insulating film.
7. The sensor according to claim 1, wherein at least part of the
plurality of insulator portions and the second insulating film are
integrated.
8. An imaging system comprising: a solid-state image sensor defined
in claim 1; and a signal processing unit which processes a signal
obtained by the solid-state image sensor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a solid-state image sensor
and an imaging system having the solid-state image sensor and, more
particularly, to the pixel structure of the solid-state image
sensor.
[0003] 2. Description of the Related Art
[0004] As solid-state image sensors used in imaging systems such as
a digital camera and camcorder are gaining smaller sizes and more
pixels, the pixel size shrinks rapidly. A smaller pixel size leads
to a smaller area of the light receiving portion of a photoelectric
conversion element in the pixel, decreasing the sensitivity of the
photoelectric conversion element. To suppress the decrease in the
sensitivity of the photoelectric conversion element, a technique of
forming an on-chip microlens on the light incident surface of a
pixel has already been in practical use. Recently in some
arrangements, a light waveguide is formed between a microlens and a
photoelectric conversion element to collect light using total
reflection of light. Japanese Patent Laid-Open No. 2007-201091
discloses a structure in which a light waveguide is formed by
filling a through hole 41 formed in a planarizing layer with a
high-refractive-index material, and covering the upper surface of
the planarizing layer with a high-refractive-index material.
[0005] However, in the structure disclosed in Japanese Patent
Laid-Open No. 2007-201091, light propagates while being reflected
by the upper and lower surfaces of the high-refractive-index
material layer arranged on the planarizing layer between adjacent
light waveguides. As a result, light may enter the light waveguide
and further the photoelectric conversion element. This may cause
mixture of colors or a noise component.
SUMMARY OF THE INVENTION
[0006] The present invention provides a technique that is
advantageous to reducing noise such as mixture of colors.
[0007] The first aspect of the present invention provides a
solid-state image sensor including a semiconductor substrate
containing a plurality of photoelectric conversion elements, the
sensor comprising a first insulating film which is arranged on the
semiconductor substrate and has a plurality of openings, each of
the plurality of openings being arranged on one of the plurality of
the photoelectric conversion elements, a plurality of insulator
portions which have a refractive index higher than a refractive
index of the first insulating film, each of the plurality of
insulator portions being arranged in one of the plurality of
openings, a second insulating film which is arranged on upper
surfaces of the plurality of insulator portions and an upper
surface of the first insulating film, and a third insulating film
which has a refractive index lower than a refractive index of the
second insulating film and is arranged in contact with an upper
surface of the second insulating film, wherein letting .lamda. be a
wavelength of light entering the plurality of insulator portions, n
be the refractive index of the second insulating film, and t be a
thickness of the second insulating film in at least part of a
region on the upper surface of the first insulating film, a
relation t<.lamda./n is satisfied.
[0008] The second aspect of the present invention provides an
imaging system comprising a solid-state image sensor defined as the
first aspect of the present invention, and a signal processing unit
which processes a signal obtained by the solid-state image
sensor.
[0009] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a sectional view exemplifying the structure of a
solid-state image sensor according to the first embodiment;
[0011] FIGS. 2A to 2D are sectional views, respectively,
exemplifying steps in manufacturing the solid-state image sensor of
FIG. 1;
[0012] FIG. 3 is a sectional view showing the structure of a
solid-state image sensor as a comparative example with respect to
the solid-state image sensor according to the embodiment in FIG.
1;
[0013] FIG. 4A is a circuit diagram exemplifying the circuit
arrangement of a pixel P in a solid-state image sensor according to
one of the first to third embodiments;
[0014] FIG. 4B is a block diagram exemplifying the configuration of
an imaging system to which the solid-state image sensor according
to one of the first to third embodiments is applied;
[0015] FIG. 5 is a sectional view exemplifying the structure of a
solid-state image sensor according to the second embodiment;
and
[0016] FIG. 6 is a sectional view exemplifying the structure of a
solid-state image sensor according to the third embodiment.
DESCRIPTION OF THE EMBODIMENTS
[0017] Preferred embodiments of the present invention will now be
described with reference to the accompanying drawings.
First Embodiment
[0018] References which disclose a technique of forming a light
waveguide are Japanese Patent Laid-Open Nos. 2003-224249 and
2006-049825. Japanese Patent Laid-Open No. 2003-224249 discloses a
structure which increases the light collection efficiency by
tapering a waveguide to widen the opening at its upper portion.
Japanese Patent Laid-Open No. 2006-049825 discloses a structure in
which a lens is further formed on a light waveguide to converge
light on it.
[0019] However, in the structure of Japanese Patent Laid-Open No.
2003-224249, light obliquely entering a condenser lens at the top
or light entering the space between adjacent condenser lenses
becomes one which does not enter the opening of the light waveguide
having a multistage opening. The light which does not enter the
opening of the light waveguide enters an adjacent element portion,
causing mixture of colors or a noise component. In the structure of
Japanese Patent Laid-Open No. 2006-049825, a condenser lens is
formed integrally with a light waveguide using the same material at
the upper portion of the opening of the light waveguide. However,
light which obliquely enters the lens and cannot be converged to
the light waveguide enters an adjacent element portion. The light
which enters the adjacent element portion becomes a noise component
to decrease the resolution or, in a color solid-state image sensor,
generate mixture of colors.
[0020] The first embodiment provides a solid-state image sensor
capable of efficiently capturing light and suppressing incidence of
light on an adjacent photoelectric conversion element, and an
imaging system having the solid-state image sensor.
[0021] <Example of Structure of Solid-State Image Sensor
According to First Embodiment>
[0022] FIG. 1 is a schematic sectional view showing a solid-state
image sensor according to the first embodiment. The first
embodiment is related to a CMOS solid-state image sensor. FIG. 1
shows the section of two pixels. A plurality of pixels as shown in
FIG. 1 are arrayed two-dimensionally and used in an imaging system
such as a digital camera or camcorder. The example of the imaging
system is described later with reference to FIG. 4B.
[0023] In FIG. 1, a photoelectric conversion element 2 and element
isolation region 3 are formed in the upper surface of a
semiconductor substrate 1. A first insulating film 100 having an
opening 101 arranged on the photoelectric conversion element 2 is
arranged on the semiconductor substrate 1 in which the
photoelectric conversion element 2 is formed. In the example shown
in FIG. 1, the first insulating film 100 includes a first
insulating layer 4, second insulating layer 6, and third insulating
layer 8. The first insulating layer 4, second insulating layer 6,
and third insulating layer 8 respectively have openings that form
the opening 101. More specifically, the first insulating layer 4
having an opening is formed on the photoelectric conversion element
2. A first wiring layer 5, and the second insulating layer 6 which
covers the first wiring layer 5 and has an opening above the
photoelectric conversion element 2 are formed on the first
insulating layer 4. A second wiring layer 7 is formed in the second
insulating layer 6. The second wiring layer 7 has a damascene
structure. The third insulating layer 8 which covers the second
insulating layer 6 and has an opening above the photoelectric
conversion element 2 is formed. The openings of the first
insulating layer 4, second insulating layer 6, and third insulating
layer 8 which correspond to the photoelectric conversion element 2
have a tapered shape to increase the area with distance from the
photoelectric conversion element 2. The openings are filled with an
insulator serving as a high-refractive-index portion formed from a
material higher in refractive index than the constituent materials
of the first insulating layer 4, second insulating layer 6, and
third insulating layer 8. The insulator forms light waveguides 9a
and 9b.
[0024] Passivation films 10a and 10b are arranged on the light
waveguide 9b as the second insulating film formed from a material
having a refractive index equal to or higher than that of the
high-refractive-index portion. In this case, let .lamda. be the
wavelength of light entering the light waveguide (insulator), and n
be the refractive index of the passivation film. Letting t1 be the
thickness of the passivation film 10a, all or at least part of the
region on the upper surface of the light waveguide is covered with
the passivation film 10a whose thickness satisfies t1>.lamda./n.
A region of the upper surface of the light waveguide that is
covered with the passivation film 10a is defined as the first
region. Also, letting t2 be the thickness of the passivation film
10b, at least part of the region on the upper surface of the first
insulating film 100 (or the third insulating layer 8) positioned
between the passivation films 10a is covered with the passivation
film 10b whose thickness satisfies t2<.lamda./n. A region of the
upper surface of the first insulating film 100 (or the third
insulating layer 8) that is covered with the passivation film 10b
is defined as the second region.
[0025] In the example shown in FIG. 1, the passivation films 10a
and 10b are formed from the same film at the predetermined
thicknesses t1 and t2, respectively. A planarizing layer 11 as the
third insulating film formed from, for example, a transparent
polymer resin having a refractive index of 1.5 is arranged on the
passivation films 10a and 10b. Further, a red color filter layer
12R and green color filter layer 12G each formed from, for example,
a transparent polymer resin having a refractive index of 1.55 are
arranged on the planarizing layer 11 in correspondence with pixels.
On-chip microlenses 13 formed from, for example, a transparent
polymer resin having a refractive index of 1.6 are arranged on the
color filter layers 12R and 12G. Needless to say, the color filter
layer may be a blue color filter layer 12B or a color filter layer
of a complementary color or the like. Hence, the color filter layer
exists above the passivation film and below the microlens. Note
that a planarizing layer may be further formed on the color filter
layer. The above-described relations t1>.lamda./n and
t2<.lamda./n are preferably satisfied in the entire band of
light which passes through the color filter layer and enters the
light waveguide (insulator).
[0026] (Example of Material of Each Element)
[0027] As the photoelectric conversion element 2, a photodiode
having a P-N junction or PIN junction, a phototransistor, or the
like is available. When light enters the semiconductor junction of
such an element, the incident light causes photoelectric
conversion, generating charges. The element isolation region 3
around each photoelectric conversion element 2 is formed by a field
oxide film formed by selective oxidation, a diffusion layer for
junction isolation, a buried element isolation method, or the like.
Note that the element isolation region 3 may achieve isolation by
impurity diffusion using a PD junction. The first insulating layer
4 covers each photoelectric conversion element 2 and the element
isolation region 3. Note that, for example, a gate insulating film
and gate electrode may be interposed between the semiconductor
substrate 1 and the first insulating layer 4. The first wiring
layer 5 has a wiring pattern. The materials of the first insulating
layer 4, second insulating layer 6, and third insulating layer 8
suffice to be transparent materials capable of transmitting light
which is absorbed in the photoelectric conversion element 2 and
converted into an electrical signal. For example, most solid-state
image sensors are used to detect visible or infrared light, so the
materials suffice to transmit these light components. The first
insulating layer 4, second insulating layer 6, and third insulating
layer 8 adopt an inorganic or organic insulator generally used as
an electrical insulating layer or passivation layer. Examples of
the materials of the first insulating layer 4, second insulating
layer 6, and third insulating layer 8 are silicon oxide or
materials each prepared by doping phosphorus, boron, fluorine,
carbon, or the like in silicon oxide. The first wiring layer 5 and
second wiring layer 7 may have aluminum patterns or copper patterns
formed by a damascene process. Examples of the material of the
high-refractive-index portion which form the light waveguides 9a
and 9b are silicon nitride having a refractive index of 2.0 and
silicon oxynitride having a refractive index of 1.8. Note that a
contact plug and via plug (neither is shown) are arranged in the
first insulating layer 4 and second insulating layer 6.
[0028] <Example of Photoelectric Conversion Element
Manufacturing Process According to First Embodiment>
[0029] FIGS. 2A to 2D are sectional views, respectively, showing
manufacturing steps in forming a light waveguide 9. Note that the
steps of forming a element in the substrate, a first insulating
layer 4, second insulating layer 6, first wiring layer 5, second
wiring layer 7, contact plug, and via plug on a semiconductor
substrate 1 are well known, and a description thereof will be
omitted.
[0030] In FIG. 2A, after forming a first wiring layer 5 and second
wiring layer 7, a photoresist is applied, and a photoresist pattern
14 is formed from the photoresist using a patterning technique in
order to form the light waveguide 9a. Then, the second insulating
layer 6 and first insulating layer 4 are etched by plasma etching.
By this etching, openings corresponding to the photoelectric
conversion element 2 are formed in the second insulating layer 6
and first insulating layer 4 and extend through them. Thereafter,
the photoresist pattern 14 is removed, obtaining a structure in
FIG. 2B. When the second insulating layer 6 is made of plasma
silicon oxide and the first insulating layer 4 is made of BPSG,
plasma etching is executed using a CF-based gas typified by
C.sub.4F.sub.8 or C.sub.5F.sub.8, O.sub.2, and Ar. Depending on
etching conditions, the second insulating layer 6 and first
insulating layer 4 can also be etched into a tapered shape in which
the opening area at the lower portion is smaller than that at the
upper portion, as shown in FIG. 2B. However, the opening is not
always limited to the tapered shape as shown in FIG. 2B.
[0031] In FIG. 2B, a high-refractive-index material (insulator) is
filled, forming a high-refractive-index portion, that is, a first
light waveguide 9a in FIG. 2C. For example, the opening is filled
with silicon nitride having a refractive index of 2.0 or silicon
oxynitride having a refractive index of 1.8 by high-density plasma
CVD, or a material having a high refractive index of 1.7 by spin
coating. After filling the high-refractive-index material, the
upper portion may be planarized using resist etch-back or CMP, as
needed. Further, plasma silicon oxide is deposited as the third
insulating layer 8, obtaining a structure in FIG. 2C.
[0032] In FIG. 2C, a high-refractive-index portion, that is, a
second light waveguide 9b is formed by photoresist patterning,
etching, and filling with a high-refractive-index material
(insulator), similar to the first light waveguide 9a. The opening
of the second light waveguide 9b serves as that of the third
insulating layer 8. At this time, the taper angles of the first
light waveguide 9a and second light waveguide 9b toward the
photoelectric conversion element may be equal or different. The
high-refractive-index portions of the first light waveguide 9a and
second light waveguide 9b are preferably formed from materials
having the same refractive index to reduce reflection at the
interface between these two high-refractive-index portions.
However, the refractive indices may not be equal. If the refractive
indices of these two high-refractive-index portions are greatly
different from each other, an antireflection film may be arranged
at the interface between the first light waveguide 9a and the
second light waveguide 9b.
[0033] After forming the light waveguide 9b, a passivation film is
formed from plasma silicon nitride having a refractive index of 2.0
or plasma silicon oxynitride having a refractive index of 1.8.
Then, a photoresist is applied to form a passivation film at the
thickness t1 in all or part of the region on the light waveguide 9b
and form it at the thickness t2 in the remaining region. The
passivation film is etched by plasma etching to have a desired
thickness. This state is a structure shown in FIG. 2D.
[0034] As the passivation film forming method, for example, a
passivation film is formed on the entire surface to have the
thickness t1, and is etched in the second region using the
photoresist pattern as the mask of the first region, obtaining
passivation films having the thicknesses t1 and t2. Passivation
films having the thicknesses t1 and t2 can also be obtained by
forming a passivation film thicker than the thickness t1, and then
performing desired photoresist patterning and etching. Further,
passivation films may be formed from two different films. For
example, after forming a film from plasma silicon oxynitride to
have the thickness t2, a film may be formed from plasma silicon
nitride to have the thickness t1, and the plasma silicon nitride
film may be patterned.
[0035] The light waveguides 9a and 9b have interfaces between the
first to third insulating layers and the high-refractive-index
materials. Thus, light entering the insides of the light waveguides
9a and 9b is totally reflected by the side surface according to
Snell's law. For example, the high-refractive-index material of the
light waveguides 9a and 9b is a plasma SiN film having a refractive
index of 2.0. The materials which form the first insulating layer
4, second insulating layer 6, and third insulating layer 8 are BPSG
(BoroPhosphoSilicate Glass) having a refractive index of 1.46, SiO
(Silicon Oxide) having a refractive index of 1.46, and SiO (Silicon
Oxide) having a refractive index of 1.46, respectively. In this
case, for light which enters the side walls of the light waveguides
9a and 9b at an incident angle of 46.9.degree. or more, the light
is totally reflected by the side walls of the light waveguides 9a
and 9b. The light totally reflected by the side wall finally enters
the photoelectric conversion element 2. By forming the light
waveguides 9a and 9b, light can effectively enter the photoelectric
conversion element 2, contributing to photoelectric conversion.
[0036] The passivation films 10a and 10b are formed to cover the
upper portion of the light waveguide and other portions. The upper
portion of the light waveguide 9b is covered with the passivation
film 10a formed from a plasma silicon nitride film having the
thickness t1 and a refractive index of 2.0. The remaining portion
except for the upper portion of the light waveguide is covered with
the passivation film 10b formed from a plasma silicon nitride film
having the thickness t2 and a refractive index of 2.0. The
planarizing layer 11 is, therefore, lower in refractive index than
the passivation film 10a. At this time, t1 suffices to be larger
than 380/2.0=190 nm because incident light has a wavelength of 380
nm (blue) or more. More preferably, t1 is larger than 600/2.0=300
nm with respect to 600 nm (red) which is almost the upper limit of
the wavelength of incident light. t2 suffices to be smaller than
380/2.0=190 nm when the wavelength of incident light is 380 nm
(blue). More preferably, t2 is equal to or larger than 30 nm and
equal to or smaller than 190 nm at which the hydrogen termination
as the function of the passivation film exhibits the dark current
reduction effect. The light collection effect according to the
first embodiment becomes more significant for a larger oblique
component of incident light.
[0037] <Effects of First Embodiment>
[0038] FIG. 3 is a sectional view of a comparative example for
explicitly explaining the effects of the photoelectric conversion
element according to the first embodiment. FIG. 3 is a sectional
view showing two adjacent pixels having the same structure as that
of the photoelectric conversion element in the first embodiment
except that a passivation film 10 is formed at a constant
thickness. In the comparative example of FIG. 3, incident light C1
enters the left part of the surface of the microlens 13 while
inclining to the left. This light is refracted by the microlens 13,
enters the opening at the upper portion of the light waveguide 9b,
and then enters the photoelectric conversion element 2. In
contrast, light C2 which enters the right part of the surface of
the microlens 13 while inclining to the left does not enter the
opening at the upper portion of the light waveguide 9b, deviates
from the light waveguide 9a, and cannot be converged. Light which
is not guided to the photoelectric conversion element 2 cannot be
effectively used for detection, and causes mixture of colors upon
entering the photoelectric conversion element 2 of an adjacent
pixel. Also, light which is not guided to the photoelectric
conversion element 2 may propagate through the passivation film 10
while being reflected, and enter another photoelectric conversion
element 2.
[0039] To the contrary, in the structure of the first embodiment
shown in FIG. 1, not only the light beam C1 but also the incident
light C2 can be guided to the opening at the upper portion of the
light waveguide 9b by total reflection because of the refractive
index difference between the passivation film 10a and the
planarizing layer 11. After that, the incident light can be totally
reflected by the side wall of the light waveguide 9a and converged
to the photoelectric conversion element 2. Even for incident light
C3, the thickness of the passivation film 10b satisfies the
relation t2<.lamda./n, so light entering the passivation film
10b from the passivation film 10a cannot propagate through the
passivation film 10b. That is, the solid-state image sensor in the
first embodiment can use the passivation films 10a and 10b
different in thickness and the light waveguide 9 to guide, to the
photoelectric conversion element, incident light which has not been
converted conventionally. Further, the solid-state image sensor in
the first embodiment can reduce light which may enter an adjacent
pixel conventionally.
[0040] The light waveguides 9a and 9b and passivation films 10a and
10b having high refractive indices may be formed from an integral
film.
Second Embodiment
[0041] FIG. 5 is a schematic sectional view showing a solid-state
image sensor according to the second embodiment. The solid-state
image sensor of the second embodiment is obtained by removing the
third insulating layer 8 and the light waveguide 9b formed in the
opening of the third insulating layer 8 from the solid-state image
sensor of the first embodiment. In the solid-state image sensor of
the second embodiment, a passivation film serving as the second
insulating film is formed from a passivation film 10b which has a
smooth continuous surface as an upper surface and has the thickness
t2. The remaining structure is the same as that in the first
embodiment. Letting t2 be the thickness of the passivation film
10b, all or at least part of the region on the upper surface of a
first insulating film 100 is covered with the passivation film 10b
whose thickness satisfies the relation t2<.lamda./n. In the
example shown in FIG. 5, the upper surfaces of the first insulating
film 100 and light waveguide 9a are covered with the passivation
film 10b which has a smooth continuous surface as an upper surface
and has the thickness t2. In the claims, this relation is described
as t<.lamda./n by replacing t2 with t for descriptive
convenience. Arranging the second insulating film, which satisfies
t2<.lamda./n (or t<.lamda./n), in all or at least part of the
region on the upper surface of the first insulating film 100
suppresses propagation of light which is reflected by the upper and
lower surfaces of the second insulating film. This suppresses
entrance of such light into a light waveguide 9a and further into a
photoelectric conversion element 2, reducing mixture of colors and
noise.
[0042] The light waveguide 9a and passivation film 10b having high
refractive indices may be formed from an integral film. A
planarizing layer 11 is not limited to a transparent polymer resin,
but may be formed from an inorganic material such as silicon oxide.
In the structure of the second embodiment, the upper surface of the
passivation film 10b is flat, so the planarizing layer 11 may not
have a planarizing function.
Third Embodiment
[0043] FIG. 6 is a schematic sectional view showing a solid-state
image sensor according to the third embodiment. In the solid-state
image sensor of the third embodiment, a passivation film serving as
the second insulating film is formed from a passivation film 10b
which has a smooth continuous surface as an upper surface and has
the above-mentioned thickness t2. The remaining structure is the
same as that in the first embodiment. Letting t2 be the thickness
of the passivation film 10b, all or at least part of the region on
the upper surface of a first insulating film 100 is covered with
the passivation film 10b whose thickness satisfies the relation
t2<.lamda./n. In the example shown in FIG. 6, the upper surface
of the first insulating film 100 and that of a light waveguide 9b
are covered with the passivation film 10b which has a smooth
continuous surface as an upper surface and has the thickness t2. In
the claims, this relation is described as t<.lamda./n by
replacing t2 with t for descriptive convenience. Arranging the
second insulating film, which satisfies t2<.lamda./n (or
t<.lamda./n), in all or at least part of the region on the upper
surface of the first insulating film 100 suppresses propagation of
light which is reflected by the upper and lower surfaces of the
second insulating film. This suppresses entrance of such light into
a light waveguide 9a and the light waveguide 9b and further into a
photoelectric conversion element 2, reducing mixture of colors and
noise.
[0044] The light waveguide 9b and passivation film 10b having high
refractive indices may be formed from an integral film. A
planarizing layer 11 is not limited to a transparent polymer resin,
but may be formed from an inorganic material such as silicon oxide.
In the structure of the third embodiment, the upper surface of the
passivation film 10b is flat, so the planarizing layer 11 may not
have a planarizing function.
[0045] <Example of Circuit Arrangement>
[0046] FIG. 4A is a circuit diagram exemplifying the typical
circuit arrangement of one pixel P in a solid-state image sensor
100 according to one of the first to third embodiments. In an
actual solid-state image sensor 100, pixels P are arrayed two- or
one-dimensionally, and a scan circuit, readout circuit, output
amplification circuit, and the like for driving a pixel are
arranged around the array. In the example of FIG. 4A, the pixel P
includes a photoelectric converter 31, transfer transistor 32,
floating diffusion (to be referred to as an FD) 33, reset
transistor 34, amplification transistor 36, and selection
transistor 35.
[0047] When light enters the light receiving surface of the
photoelectric converter 31, the photoelectric converter 31
generates charges (electrons in this example) corresponding to the
light and stores them. The photoelectric converter 31 is, for
example, a photodiode, and stores, in the cathode, charges
generated by photoelectric conversion performed at the interface
between the anode and the cathode. When the channel is rendered
conductive (rendering the transistor conductive will be described
as "turning on the transistor", and rendering the transistor
non-conductive will be described as "turning off the transistor"),
the transfer transistor 32 transfers charges generated in the
photoelectric converter 31 to the FD 33. When the reset transistor
34 is turned on, it resets the FD 33. The amplification transistor
36 outputs a signal corresponding to the potential of the FD 33 to
a vertical signal line 37 by performing a source follower operation
together with a constant current source 38 connected to the
vertical signal line 37. The vertical signal line 37 is connected
to other pixels in the column direction and shared between a
plurality of pixels. That is, when the reset transistor 34 resets
the FD 33, the amplification transistor 36 outputs a noise signal
corresponding to the potential of the FD 33 to the vertical signal
line 37. When the transfer transistor 32 transfers charges
generated in the photoelectric converter 31 to the FD 33, the
amplification transistor 36 outputs an optical signal corresponding
to the potential of the FD 33 to the vertical signal line 37. The
selection transistor 35 selects the pixel P when it is turned on,
and cancels selection of the pixel P when it is turned off. Note
that when the selected state/unselected state of the pixel P is
controlled based on the potential of the FD 33, the selection
transistor 35 may be omitted from the pixel P and a plurality of
photoelectric converters 31 may be arranged for one amplification
transistor 36. For example, a readout circuit 39 reads out the
signals of a plurality of pixels in the column direction along the
vertical signal line 37 as a one-dimensional image sensing result
or composites them with those along another vertical signal line 37
in the row direction and reads outs them as a two-dimensional image
sensing result, and the solid-state image sensor outputs the result
as an output signal, details of which will not be described. The
reset signal, the transfer signal, and the pixel selection signal
shown in FIG. 4A are examples of a signal that controls the
operation of each transistor.
[0048] <Example of Configuration of Imaging System>
[0049] FIG. 4B exemplifies the configuration of an imaging system
to which the solid-state image sensor 100 according to one of the
first to third embodiments is applied. An imaging system 90 mainly
includes an optical system, image sensing unit 86, and signal
processing unit. The optical system mainly includes a shutter 91,
lens 92, and stop 93. The image sensing unit 86 includes the
solid-state image sensor 100 of the embodiment. The signal
processing unit mainly includes a sensed signal processing circuit
95, A/D converter 96, image signal processor 97, memory 87,
external I/F 89, timing generator 98, overall control/arithmetic
unit 99, recording medium 88, and recording medium control I/F 94.
The signal processing unit may not include the recording medium 88.
The shutter 91 is arranged in front of the lens 92 on the optical
path to control the exposure. The lens 92 refracts incident light
to form an object image on the image sensing surface of the
solid-state image sensor 100 of the image sensing unit 86. The stop
93 is interposed between the lens 92 and the solid-state image
sensor 100 on the optical path. The stop 93 adjusts the quantity of
light guided to the solid-state image sensor 100 after the light
passes through the lens 92.
[0050] The solid-state image sensor 100 of the image sensing unit
86 converts an object image formed on the image sensing surface of
the solid-state image sensor 100 into an image signal. The image
sensing unit 86 reads out the image signal from the solid-state
image sensor 100, and outputs it. The sensed signal processing
circuit 95 is connected to the image sensing unit 86, and processes
an image signal output from the image sensing unit 86. The A/D
converter 96 is connected to the sensed signal processing circuit
95. The A/D converter 96 converts a processed image signal (analog
signal) output from the sensed signal processing circuit 95 into an
image signal (digital signal). The image signal processor 97 is
connected to the A/D converter 96. The image signal processor 97
performs various arithmetic processes such as correction for an
image signal (digital signal) output from the A/D converter 96,
generating image data. The image signal processor 97 supplies the
image data to the memory 87, external I/F 89, overall
control/arithmetic unit 99, recording medium control I/F 94, and
the like. The memory 87 is connected to the image signal processor
97, and stores image data output from the image signal processor
97. The external I/F 89 is connected to the image signal processor
97. Image data output from the image signal processor 97 is
transferred to an external device (for example, a personal
computer) via the external I/F 89.
[0051] The timing generator 98 is connected to the image sensing
unit 86, sensed signal processing circuit 95, A/D converter 96, and
image signal processor 97. The timing generator 98 supplies timing
signals to the image sensing unit 86, sensed signal processing
circuit 95, A/D converter 96, and image signal processor 97. The
image sensing unit 86, sensed signal processing circuit 95, A/D
converter 96, and image signal processor 97 operate in synchronism
with the timing signals. The overall control/arithmetic unit 99 is
connected to the timing generator 98, image signal processor 97,
and recording medium control I/F 94, and controls all of them. The
recording medium 88 is detachably connected to the recording medium
control I/F 94. Image data output from the image signal processor
97 is recorded on the recording medium 88 via the recording medium
control I/F 94.
[0052] With this arrangement, the solid-state image sensor 100 can
provide a high-quality image (image data) in the imaging system as
long as it can obtain a high-quality image signal.
[0053] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0054] This application claims the benefit of Japanese Patent
Application No. 2010-088192, filed Apr. 6, 2010 and No.
2011-026532, filed Feb. 9, 2011, which are hereby incorporated by
reference herein in their entirety.
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